A simple and accurate numeric solution procedure for nonlinear buckling model of drill string with frictional effect

• Nonlinear buckling of drill string with frictional effect is studied.
• Numeric solutions are obtained by the extended system shooting method.
• The solution procedure of the present method is brief.
• Compared to existing solutions, the accuracy of the present one is substantiated.

The nonlinear buckling analysis of drill string in a rigid well is presented in this paper. Considering effects of friction and boundary constraints, this problem could be taken as a model of a rod laterally constrained in a rigid cylinder (horizontal, oblique and vertical rigid cylinder could be included). After introducing a new variable, the resulting coupled nonlinear integral–differential equations are successfully solved by employing the extended system shooting method. Examples with various friction coefficients and combinations of boundary conditions are proposed. It is found that the axial frictional force plays a more significant part on buckling load for horizontal well than vertical one. Compared to experimental data or results obtained by using the discrete singular convolution algorithm (DSC) and the finite element method (FEM), the accuracy of the formulations and solution procedures, is verified. What’s more, the nonlinear buckling behaviors of two instances of vertical scientific wells are analyzed. The present results are useful for practical design applications related to calculation of buckling loads and selection of bottom hole assembly (BHA) elements.

By introducing a new variable and using the extended system shooting method, nonlinear buckling behavior of drill string with frictional effect (horizontal, oblique and vertical wellbore could be included), is investigated.Figure optionsDownload as PowerPoint slide